Identifying priorities for the joint conservation of maritime built heritage and marine biodiversity: An assessment of shoreline engineering on the Isles of Scilly, UK, using historical datasets

Growing concern over the ecological impact of maritime structures has led to increasing attempts to quantify the extent of marine human development. However, maritime heritage assets (i.e., historic structures of cultural significance, such as decommissioned quays) are often missing in these assessments as many of these structures are not recorded in conventional datasets of maritime infrastructure, instead featuring exclusively in heritage registers. At the same time, heritage assets may provide unintentional ecological benefits to marine wildlife due to their age, traditional construction, and protected status, and as such, comprehensive assessments of marine human development cannot be achieved without the inclusion of historical data. Using the Isles of Scilly as a geographically confined case study, we present a novel methodology for quantifying the full extent of marine engineering structures (including heritage assets) at a regional scale, and for identifying priority structures for joint biodiversity and heritage conservation. Historical datasets were considered alongside remote sensing data and records of modern coastal defences in a rapid desk-based assessment to create a full inventory of marine structures along the entire coastline of the Isles of Scilly. In total, 68 structures were recorded, totalling 6180 m in length. By evaluating the ecological potential and heritage value of each structure using a novel scoring system that was verified in the field, priorities for conservation and other managed interventions are identified. This includes (1) listed buildings and scheduled monuments that due to their construction features and shore position are most likely to support diverse marine assemblages, and (2) modern structures where eco-enhancement adaptations may be favourable. As demonstrated here, combined ecological-heritage evaluations allow for the identification of structures with the greatest potential for the joint conservation of built heritage and marine wildlife. Research is now needed to develop this method further and test its application in other geographical locations and at varying spatial scales.